1. Field of the Invention
The present invention relates to an improvement in a frame assembly for a motorcycle.
2. Description of the Background Art
It is well known to form the frame assembly of a motorcycle by casting the frame from an aluminum alloy. It is also well known to provide a single leading frame portion of the motorcycle frame assembly which extends rearwardly from a head pipe. Such a frame assembly is disclosed, for example, in Japanese Utility Model Laid-open No. Hei 1-68293.
The following discussion refers to, and uses reference numbers from, the drawings of Japanese Utility Model Laid-open No. Hei 1-68293. As shown in FIGS. 1 and 3 of Japanese Utility Model Laid-open No. Hei 1-68293, a frame 10 is a member cast from an aluminum alloy, which is composed of a member 20 and a member 40 split to the left and the right, wherein respective front half portions 23 and 43 (for symbol 43, see FIG. 4) extending from the side of a head tube 21 are rectilinear, respective rear half portions 24 and 44 are dividedly extended to the outer sides and are angled rearwardly downward side from the rear ends of the front half portions 23 and 43, and the left and right front half portions 23 and 43 constitute a single main frame.
While the frame 10 is composed of the left and right two component parts, the structure, which is split to the left and the right, has the following problem: That is, left-right assembly error or errors are liable to be generated between the member 20 and the member 40. For example, it is difficult to accurately match the positions in the front-rear direction of left and right pivot portions 28 and 48 for supporting a rear swing arm 6 (see FIG. 1), or to accurately arrange the rear half portion 24 and the rear half portion 44 in left-right symmetry with respect to the center line extending in the front-rear direction of the frame 10. In addition, since the frame 10 is long in the front-rear direction, the length of weld that joins the member 20 and the member 40 to each other is large. As a result, the welding operation is lengthy so that manufacturing productivity is lowered.
It is an object of the present invention to provide an improved frame assembly for a motorcycle, in which the frame assembly is formed more accurately, and in which the manufacturing productivity of the frame assembly is enhanced.